1. Field of the Invention
This invention relates to a poly-silicon display device, and more particularly to a poly-silicon liquid crystal display and a simplified method of fabricating the same.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device, which includes a plurality of liquid crystal cells in a matrix configuration in a liquid crystal display panel, displays images by controlling the transmittance of light in accordance with video signals. In each liquid crystal cell, a thin film transistor (TFT) is used as a switching device to independently supply a video signal. An active layer of such a TFT is generally formed of either amorphous silicon or polycrystalline silicon (poly-silicon). Because the carrier mobility of poly-silicon is approximately hundred times faster than the carrier mobility of amorphous silicon, high-speed driving circuits can be integrally formed in the LCD panel with the poly-silicon technology.
FIG. 1 is a schematic view illustrating a TFT substrate of a poly-silicon liquid crystal display panel integrated with driving circuits according to the related art.
Referring to FIG. 1, the TFT substrate includes a display area 7 provided with a TFT 30 and a pixel electrode 22 in each pixel area defined by the crossings of gate lines 2 and data lines 4, a data driver 5 for driving the data lines 4, and a gate driver 3 for driving the gate lines
The TFT 30 charges a video signal from the data line 4 into the pixel electrode 22 in response to a scanning signal from the gate line 2. The pixel electrode 22 charged with the video signal generates a potential difference with respect to a common electrode of a color filter substrate which faces the TFT substrate with liquid crystal therebetween. This potential difference rotates the molecules of the liquid crystal due to the dielectric anisotropy of the liquid crystal. The transmittance of light varies depending on an amount of rotation of the liquid crystal molecules, thereby implementing gray-scale levels.
The gate driver 3 sequentially drives the gate lines 2, and the data driver 5 applies video signals to the data lines 4 when one of the gate lines 2 is driven.
FIG. 2 is an enlarged plan view of one pixel area included in the display area 7 of the TFT substrate illustrate in FIG. 1, and FIG. 3 is a cross-sectional view of the pixel area of the TFT substrate taken along the line I-I′ in FIG. 2.
Referring to FIGS. 2 and 3, the TFT substrate includes the thin film transistor (TFT) 30 connected to the gate line 2 and the data line 4, and the pixel electrode 22 connected to the TFT 30. Although either an NMOS-TFT or PMOS-TFT can be used for the TFT 30, the TFT 30 employing an NMOS-TFT will now be described.
The TFT 30 has a gate electrode 6 connected to the gate line 2, a source electrode connected to the data line 4, and a drain electrode 10 connected to the pixel electrode 22 via a pixel contact hole 20 passing through a protective film 18. The gate electrode 6 overlaps a channel area 14C of an active layer 14 provided on a buffer film 12 with a gate insulating film 16 therebetween. The source electrode and the drain electrode 10 are formed in such a manner to be insulated from the gate electrode 6 with an interlayer insulating film 26 therebetween. Further, the source electrode and the drain electrode 10 are connected to a source area 14S and a drain area 14D of the active layer 14 doped with an n+ impurity, respectively, via a source contact hole 24S and a drain contact hole 24D passing through the interlayer insulating film 26 and the gate insulating film 16.
The TFT substrate according to the related art has a problem in that the manufacturing process is complicated and the manufacturing cost is high.